The present invention is directed to a chopping energization control device including a switching element interposed between one end of an electric coil of a motor and one terminal of a power supply and another switching element interposed between the other end of the electric coil of the motor and the other terminal of the power supply and energizing the electric coil in chopping mode in such a manner that both of the switching elements are turned on and off (are made to be conductive and nonconductive), the motor is in synchronization, and such operations are repeated. This chopping energization device is used, for example, to energize each of plural phase coils of an SR motor (Switched Reluctance Motor).
For example, an energizing device for SR motor such as an SR motor driver makes switching plural phases (e.g. three phases) or switching energization (ON) of the phase coil (electric coil) and de-energization (OFF) of the phase coil (electric coil). In addition, in order to derive a required torque from the SR motor, ON/OFF control is conducted for maintaining a target current in such a manner that a chopping operation or alternating turn-on and off operation is made on a pair of switching elements allocated to each of the phase coils or an upper sided one of the switching elements. For maintaining or controlling the motor current at the target current amount, some modes have been provided. One of them is soft chopping mode, another is hard chopping mode, and a combination of these modes established depending on motor conditions. These modes are disclosed in detail in Japanese Patent laid-open print No. Hei.8(1996)-172793. The soft chopping mode is to make chopping on one of the pairs of switching elements allocated to each of the phase or electric coils. The hard chopping mode is to turn on and off both of the switching elements in synchronizing fashion.
In addition to the aforementioned soft chopping mode and hard chopping mode, in recent years, compulsory soft chopping mode, frequency reduction mode, and 0V loop soft chopping mode have been provided. The compulsory soft chopping mode is, for the reduction of noise upon switching from one to another the phase coil that is to be energized, to turn on and off one of the switching elements cyclically in compulsion while the other of the switching elements is being turned on in continual fashion. The frequency reduction mode is to lower the chopping frequency so as to prevent overheat of the switching circuit for chopping control or motor driver. The 0V loop soft chopping mode, for raising electric consumption efficiency, is to drive the motor in a very short time of the switching element by the consumption of the electromagnetic at the phase coil which has been stored therein as a result of turning off of upside energizing circuit which is earlier than the ordinal energization off timing.
However, none of these modes are valid throughout all driving stages of the electric motor. For example, lowering the chopping frequency for the protection of the switching circuit from heat generated brings in torqwue variation. The compulsory soft chopping mode is ineffective when the electric motor is in a stage when the energization is made for a very short time or when the current is required to be high in magnitude. In addition, in cases where the 0V loop soft chopping mode is used when the motor is driven to start the electric powered vehicle, if the rotor is resting at an angular position which turns off only the upside energization circuit, no current flows through the electric motor, which results in the motor failing to start.
It is, therefore, a principal objective of the present invention to provide a chopping energization control device which makes it possible to drive an electric motor in smooth fashion while restricting of a motor drive resulting from chopping energization.
A second objective of the present invention is to provide a chopping energization control device which makes it possible to drive an electric motor in smooth fashion while the chopping noise is reduced.
A third objective of the present invention is to provide a chopping energization control device which makes it possible to drive an electric motor in smooth fashion while the electric power consumption efficiency of the electric motor becomes possible to increase.
In order to attain the foregoing objectives, a first aspect of the present invention provides a chopping energization control device which comprises:
first switching means (18a) interposed between one end of an electric coil (1a, 1b, 1c) of an electric motor (1) and one terminal (18e) of a power supply;
second switching means (18b) interposed between the other end of the electric coil (1a, 1b, 1c) and the other terminal (18f) of the power supply;
signal generation means (11-17) for generating an energization indication signal (S8) which makes the first switching means (18a) and the second switching means (18b) conductive in order to establish a chopping energization of the electric coil (1a, 1b, 1c) at a chopping frequency on the basis of a target driving torque, (Trq) and a rotation number (Nm) of the electric motor (1); and
control means (11) for making the chopping frequency smaller when the rotation number, or motor speed value, (Nm) of the electric motor (1) is equal to or less than a predetermined value (w1) than when the rotation number (Nm) of the electric motor (1) is greater than the predetermined value (w1).
It is to be noted that the foregoing reference numerals and reference codes which correspond to those in the drawings and are later described are added in parentheses to facilitate easy understanding of the invention.
In accordance with the first aspect of the present invention as defined above, while the electric motor (1) operates at a low speed, the electric motor (1) is being energized for a longer time and therefore the heat generation at the switching means (18a, 18b) becomes large which are active in chopping energization. However, at this time, the chopping frequency (fc) is lowered, which makes it possible to prevent overheat of the switching means (18, 18b). On the other hand, while the electric motor (1) operates at a high speed, the electric motor (1) is being energized for a shorter time and therefore no over heat occurs at the switching means (18a, 18b) even though the chopping frequency is raised for smoothing the rotation of the electric motor (1).
A second aspect of the present invention provides a chopping energization control device which comprises:
first switching means (18a) interposed between one end of an electric coil (1a, 1b, 1c) of an electric motor (1) and one terminal (18e) of a power supply;
second switching means (18b) interposed between the other end of the electric coil (1a, 1b, 1c) and the other terminal (18f) of the power supply;
signal generation means (11-17) for generating an energization indication signal (S8) which makes the first switching means (18a) and the second switching means (18b) conductive in order to establish a chopping energization of the electric coil (1a, 1b, 1c) on the basis of a target driving torque (Trq) and a rotation number (Nm) of the electric motor (1);
a current sensor (2-4) for detecting an amount of current which flows through the electric coil (1a, 1b, 1c); and
control means (11-17) for controlling the electric coil (1a, 1b, 1c) in soft chopping mode and compulsory soft chopping mode if the target driving torque (Trq) becomes larger than a predetermined value (t1) and becomes equal to or smaller than the predetermined value (t1), respectively (Ac region, Cb region), while the electric coil (1a, 1b, 1c) is in its energization period,
the soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-on when the current amount detected by the current sensor (2) is equal to or less than a target current value corresponding to the target driving torque (Trq), while making the other of the first switching means (18a) and the second switching means (18b) being turned-on in continual fashion, the soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-off when the current amount detected by the current sensor (2) is greater than the target current value corresponding to the target driving torque, while making the other of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion, the soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-off when the current amount detected by the current sensor (2) is greater than the target current value corresponding to the target driving torque, while making the other of the of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion,
the compulsory soft chopping mode repetitively alternating turn-on and turn-off of one of the first switching means (18a) and the second switching means (18b) in compulsory fashion at a cycle (15 KHz) while making the other of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion.
In accordance with the second aspect of the present invention, in the soft chopping mode wherein one of the first switching means (18a) and the second switching means (18b) is brought into on/off chopping state while the other is in continual on state, the current ripple in the electric coil becomes little and torque variation of the electric motor becomes small, which reduce noise and vibrations, respectively. However, one of the first switching means (18a) and the second switching means (18b) under on-off chopping state are brought into electric loss concentrically, thereby becoming an easy condition of over heat. The compulsory soft chopping mode wherein one of the first switching means and the second switching means is compelled to be turned on and off in repeated fashion at a constant cycle of 15 KHz(=66 msec) is effective in noise reduction, but is invalid when energization time is short or high amount of current is required.
In the foregoing structure, the soft chopping mode is made when the electric motor is in high torque required regions, i.e. Ac region and Cb region wherein the target driving torque (Trq) exceeds the set value (t1), which makes it possible to obtain smooth high torque, thereby lowering the vibrations of the electric motor (1). As will be indicated in the seventh aspect, the concentration of electric loss on one of the first switching means (18a) and the second switching means (18b) can be avoided by replacing the same with the other in role at a cycle of time (8 msec). If lower torque is required, i.e. the target torque (Trq) is requested to be equal to or less than the set value (t1) (in Aa region and Ca region), the compulsory chopping mode is made, thereby reducing the noise. Even in the low torque region, the target current value is small, as indicated in the fourth aspect of the present invention. Because the compulsory chopping mode is only allowed in a low speed region (not greater than w2), it is possible to ensure motor drive.
A third aspect of the present invention is to provide a chopping energization control device which comprises:
first switching means (18a) interposed between one end of an electric coil (1a, 1b, 1c) of an electric motor (1) and one terminal (18e) of a power supply;
second switching means (18b) interposed between the other end of the electric coil (1a, 1b, 1c) and the other terminal (18f) bof the power supply;
signal generation means (11-17) for generating an energization indication signal (S8) which makes the first switching means (18a) and the second switching means (18b) conductive in order to establish a chopping energization of the electric coil (1a, 1b. 1c) on the basis of a target driving torque (Trq) and a rotation number (Nm) of the electric motor (1);
a current sensor (2) for detecting an amount of current which flows through the electric coil (1a, 1b, 1c); and
control means (11-17) for controlling the electric coil (1a, 1b, 1c) in soft chopping mode and 0V loop soft chopping mode if the rotation number (Nm) of the electric motor (1) is equal to or less than a predetermined value (w2) and is greater than the predetermined value (w2), respectively,
the soft chopping mode making, during an energization period of the electric coil, one of the first switching means (18a) and the second switching means (18b) turned-on when the current amount detected by the current sensor (2) is equal to or less than and greater than, respectively, a target current value corresponding to the target driving torque, while making the other of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion,
the 0V loop soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-on when the current amount detected by the current sensor (2) is equal to or less than and greater than, respectively, the target current value corresponding to the target driving torque (Trq), the turning-off being made before the termination of the energization period of the electric coil (1a, 1b, 1c), while making the other of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion during the energization period of the electric coil (1a, 1b, 1c).
The effect of the soft chopping mode when the rotation number (Nm) is equal to or less than the set value (w2) is similar to that in the second aspect of the present invention. The 0V loop soft chopping is to make the off timing of on-off chopping of one of the first switching means (18a) and the second switching means (18b) earlier when the phase energization time ends, during the remaining time ranging from the off time and the termination of the phase energization time the other switching means is turned on and the electromagnetic energy stored in the electric coil is consumed in the coil. That is to say, a current flows through the coil, which contributes driving the rotor, thereby enabling driving the motor for a short time (short phase switching cycle). Thus, the electric power consumption efficiency of the motor becomes improved. In addition, designs for increasing the number of phase and/or increasing the rotation number of the motor are possible or acceptable. Though making the off timing earlier prevents the starting motor if the rotor stops at an angle which is in coincidence with an off switching angle of the switching means, such a problem fails to occur due to the fact that the 0V loop soft chopping is made if the rotation number (Nm) exceeds the set value (w2) (in Ac region and Cc region).
A fourth aspect of the present invention is to provide a chopping energization control device which comprises:
first switching means (18a) interposed between one end of an electric coil (1a, 1b, 1c) of an electric motor (1) and one terminal (18e) of a power supply;
second switching means (18b) interposed between the other end of the electric coil (1a, 1b, 1c) and the other terminal (18f) of the power supply;
signal generation means (11-17) for generating an energization indication signal (S8) which makes the first switching means (18a) and the second switching means (18b) conductive in order to establish a chopping energization of the electric coil (1a, 1b, 1c) on the basis of a target driving torque (trq) and a rotation number (Nm) of the electric motor (1);
a current sensor (2) for detecting an amount of current which flows through the electric coil (1a, 1b, 1c) and
control means (11-17) for controlling the electric coil (1a, 1b, 1c) in soft chopping mode, compulsory chopping mode, and 0V loop soft chopping mode if the rotation number (Nm) of the motor (1) is equal to or less than a set value (w2) and the target driving torque exceeds a predetermined value (t1) while the electric coil (1a, 1b, 1c) is in its energizing period,
if the rotation number (Nm) of the motor (1) is equal to or less than the set value (w2) and the target driving torque is equal to or less than the predetermined value (t1) while the electric coil (1a, 1b, 1c) is in its energizing period, and
if the rotation number (Nm) of the motor (1) is greater than the set value (w2), respectively,
the soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-on when a value of current detected by the current sensor (2) is equal to or less than a target current value corresponding to the target driving torque, the soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-off when the value of current detected by the current sensor (2) is greater than the target current value, the soft chopping mode making the other of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion,
the compulsory soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-on when the value of current detected by the current sensor (2) is equal to or less than the set value, the compulsory soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-off when a set time (1 xcexcs) elapses after the value of current detected by the current sensor (2) becomes greater than the set value, the compulsory soft chopping mode making the other of the first switching means and the second switching means turned-on in continual fashion,
the 0V loop soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-on when the value of current detected by the current sensor (2) is equal to or less than the target current value, the 0V loop soft chopping mode making one of the first switching means (18a) and the second switching means (18b) turned-off prior to the energizing period of the electric coil (1a, 1b, 1c) when the value of current detected by the current sensor (2) is greater than the target current value, the 0V loop soft chopping mode making the other of the first switching means (18a) and the second switching means (18b) turned-on in continual fashion.
The fourth aspect of the present invention is a combination of the second aspect and the third aspect of the present invention and thus the merits and advantages of both aspects can be obtained as previously mentioned.
A fifth aspect of the present invention is to provide a chopping energization control device defined by the first aspect, the second aspect, the third aspect, and the fourth aspect of the present invention, wherein the control means (11-17), while the electric motor (1) is in regenerating mode under which a polarity of the target torque value (Trq) and a rotational direction of the electric motor (1) differs, the electric coil (1a, 1b, 1c) is controlled in hard chopping mode in such a manner that if the value of current detected by the current sensor (2) is equal to or less than and is greater than the target current value corresponding to the target driving torque (Trq), both of the first switching means (18a) and the second switching means (18b) are concurrently turned on and off, respectively.
In the regenerating condition wherein the polarity of the target driving torque (Trq) is different from the rotational direction of the electric motor e.g. in the structure of the motor driver 18 which is shown in FIG.2, in regretting condition, making both of the switching elements 18a and 18b turned off induces a current in the electric coil 1a and the resulting or induced current is fed to the lines 18e and l8f by way of the respective diodes 18c and 18d (regenerating braking). Under the resultant condition, making the switching element 18a turned on and off, which establishes generating braking wherein the switching element 18a consumes the electric power generated at the electric coil 1a, thereby making it possible to adjust the braking force. However, the switching element 18a generates heat. In the fifth aspect of the present invention, both of the switching elements 18a and 18b are turned on and off, which increases the generating braking effect. In addition, the heat is shared by both switching elements, which means that the individual switching element becomes smaller in heat generation when compared to the generating braking effect.
It is to be noted that if an H-type bridge type motor drive is employed wherein the diodes 18c and 18d are formed into switching elements, in regenerating condition, the braking force can be adjusted by controlling the regenerative electric power with doing hard chopping mode wherein a first pair of switching elements (e.g. 18a and 18b) are turned off, while a second pair of switching elements (e.g. which are replaced with the diodes 18c and 18d).
A sixth aspect of the present invention is to provide a chopping energization control device as defined in the second aspect, the third aspect, the fourth aspect, and the fifth aspect, wherein if the rotation number (Nm) of the electric motor (1) is a value which is equal to or smaller than the set value and is greater than the set value (w2), the control means(11-17) makes the frequency low and high, respectively.
In accordance with the sixth aspect of the present invention, advantages similar to those of the first aspect can be obtained.
A seventh aspect of the present invention is to provide a chopping energization control device as defined in the second aspect, the third aspect, and fourth aspect wherein at a cycle of time (8 msec) the first switching means (18a) is replaced with the second switching means (18b) so as to be turned on and off in alternate fashion while the second switching means (18b) is replaced with the first switching means (18a) so as to be turned on in continual fashion.
The switching means under on-off chopping state is large in electric loss and therefore the resulting heat generation becomes large, while the switching means which, in continual on condition, is small in electric loss and therefore the resultant heat generation becomes small. Thus, making replacement between both switching means establishes heat generation equivalence between both switching means, which makes it possible to avoid that one of the switching means is brought into over heat condition when compared to the other switching means.